ensure-directories-exist: Signal an error when trying to create a
directory with the same name as an existing file.

Previously (ensure-directories-exist "/foo/bar/"), where /foo/bar is a
regular file, just silently returned "/foo/bar/", NIL.
Merge branch 'master' into mswinmt

Conflicts:
	src/code/filesys.lisp
Make SBCL buildable by Clang.

The only changes needed were a modification to use $CC when building
contribs, and inline declaration incompatibility for a couple of
functions.

Closes lp#658414.
Merge branch 'master' into mswinmt
Closes https://bugs.launchpad.net/sbcl/+bug/911027

Fix copy-structure.  When copying from stack to heap, garbage could
end up in the heap making GC unhappy.  Thanks to James Knight.
Merge branch 'master' into mswinmt
Don't signal a note on NOTINLINE non-toplevel functions.

When a function was declared NOTINLINE, and later defined not at the
toplevel, SBCL signaled a note saying that it can't inline it.

Fixes lp#963530.
Fixup fewer complaints about hairy lexical environments

In particular, if the function has been requested NOTINLINE, and that name
has never been INLINE or MAYBE-INLINE, there should be no compiler note.
Include a test case and a NEWS entry for posterity.
Fix build on PPC/Darwin
contrib/asdf: Import asdf 2.20 from upstream.

   * lp#933112
clarify the make.sh --with-feature and --without-feature syntax in INSTALL

  Documentation-only, so going in despite the freeze.
Add an entry for ASDF upgrade to NEWS
Add workaround to a flaky semaphore timeout test.
1.0.56: will be tagged as "sbcl-1.0.56"
better REPLACE docstring

  lp#965592
sb-simple-streams: signal an error for bad stream classes in OPEN

  Instead of silently returning NIL, signal an error if the class does not
  exist (if argument :class is a symbol) or is not a stream class.

  lp#969352
don't refer to unix namestrings on windows
plain T and OTHERWISE not allowed in CASE normal-clauses

  lp#959687
more conservative classoid-name clearing

  (SETF (FIND-CLASS X) NIL) should not clear the classoid name if X is
  not the proper name of the class.

  lp#941102
MAKE-LEXENV used NCONC on its arguments, which callers did not expect

  Fixes lp#924276.